544 



TEXT-BOOK OF EMBRYOLOGY. 



differentiates various nuclei, especially those which receive the general somatic 

 sensory fibers (medial lemniscus or fillet), and other nuclei in relation to definite 

 centers of the pallium. The thalamus is thus strongly developed, owing to its 

 containing the nuclei which receive the general sensory (ventro-lateral nuclei), 

 acoustic (medial geniculate bodies), and optic (lateral geniculate bodies) 

 systems of fibers and which in turn send fibers (thalamic radiations] to the pallium. 

 These thalamic nuclei do not receive fibers probably until after the middle of the 

 second month. About this time the thalamic radiations begin to be formed 

 from the thalamic nuclei and grow toward the corpus striatum which they reach 

 toward the end of the second month. With the first appearance of the cortical 



TbaJatniis 



Bbinencephalon 



Recessus opticus 



Chiasma Opticiim .. 



Recessua infundibnli ' / 

 Infimdibulum 



Pedunculus cerebri 



Velum raedul- 

 lare anterius 



Pon, [VaroM] \M 



Ve 

 FIG. 469. Adult human brain, right half, seen from the left, partly schematic. Spalteholz. 



V;ephalon\ 



layer of the developing neopallium (see p. 549) they penetrate the corpus stria- 

 tum and pass to the cortex, forming the beginning of the internal capsule, and 

 corona radiata. It has already been pointed out (p. 474) that the great develop- 

 ment of the thalamus and its radiations is more recent phylogenetically and is 

 due to the newly acquired connections with the neopallium. 



Before the development of these neopallial connections, other tracts have 

 begun to appear which represent older epithalamic and hypothalamic connec- 

 tions existing practically throughout the Vertebrates (pp. ^474 and 475). Some 

 of the hypothalamic connections are the mammillo-tegmental fasciculus which 

 appears early in the second month, the thalamomammillary fasciculus 

 (Vicq d'Azyr's bundle), which appears later, and the bundles from the rhinen- 

 cephalon (p. 512) and archipallium (columns of the fornix, middle of fourth 

 month, p. 558). In the hypothalamic region is also differentiated the corpus 



